1. Field of the Invention
The present invention relates to an enclosed high voltage circuit breaker, particularly a circuit breaker for voltages exceeding 200 kV, containing a gaseous, fluorine-containing insulating and arc-extinguishing medium, preferably sulphur hexafluoride (SF.sub.6). The circuit breaker is of the type in which the main breaking gaps are arranged in a high-pressure chamber which is adapted, during a breaking operation, to be put in communication with a low-pressure chamber through one or more blast valves.
2. The Prior Art
In circuit breakers for the high voltages prevailing in this connection, it is often necessary to use closing resistors in order to limit the switching overvoltages upon closing. These resistors must be relatively low-ohmic (of the order of magnitude of 300-500 ohms per phase), and they must be able to conduct a relatively great current for about 10 ms. Usually such resistors are built up of ceramic resistor blocks. In sulphur hexafluoride circuit breakers, however, unprotected resistor blocks of a ceramic type will be attacked by the decomposition products produced by circuit breakers during breaking. In order to prevent this, the resistors can be cast into epoxy resin, but this involves the disadvantage that they cannot be so heavily loaded.
In a known embodiment of enclosed sulphur hexafluoride circuit breakers of the two-pressure type having low-ohmic closing resistors, the resistor elements are located in a separate tank. In this way it is possible to prevent the resistor from being subjected to the harmful affect of the decomposition products generated by the breaking arcs, and, since the resistor does not have to be cast into plastic, a relatively great energy intake may be allowed. However, in this embodiment of the circuit breaker, the contact device for the resistor has been placed in the immediate vicinity of the resistor in such a way that the resistor can be exposed to harmful decomposition products which are generated through the pre-arcs occurring during closing. Since, in addition, the contact device is positioned in low-pressure sulphur hexafluoride gas, the contact distance and thus the contact path must be made relatively long, and the casing surrounding the contact device is given relatively large dimensions.